1. Field of the Invention
This invention relates to a photosensitive member to be mounted in electrophotographic devices and others particularly a photosensitive member which is inhibited from interference of the incident light within the photosensitive member.
2. Description of the Prior Art
Laser beam printing comprises a combination of electrophotographic technique and laser technique, in which images are written by laser beam on a charged photosensitive drum to form latent images, which are in turn developed by a toner and transferred onto a transfer paper to obtain a hard copy. Since a laser beam printer is a non-impact printer, it has the advantages of smaller noise, capability of speed-up, higher quality of printed letters as compared with other non-impact printers and availability of plain papers.
However, since a laser beam is a coherent light, depending on the constitution of the photosensitive member of a photosensitive drum, multiple reflections of laser beam may occur within the photosensitive member to form interference pattern, which will disadvantageously appear on the images.
For example, as shown in the sectional view of the portion of the photosensitive drum of the prior art in FIG. 1, we now hypothesize the case in which laser beam 13a is irradiated on the photosensitive member 1 having a photoconductive member 12 provided on an electroconductive substrate 11. A laser beam consists primarily of waves with longer wavelengths and the photosensitivity of the photoconductive member 12 is frequently low relative to the light with longer wavelengths such as the laser beam 13a. In other words, the photoconductive layer 12 is smaller in absorption of the laser beam 13a and high in transmittance thereof. In such a case, the laser beam 13a incident on the photosensitive member 1 reaches the interface between the photoconductive layer 12 and the electroconductive substrate 11, where it is reflected and reaches the interface point 14.
On the other hand, the laser beam 13b which is allowed to scan over the photosensitive member 1, enter the photoconductive layer 12 at the interface point 14 and be reflected against the interface of the electroconductive substrate 11, will disadvantageously interfere with the laser beam 13a which is reflected against the aforesaid interface of the electroconductive substrate 11 and reaches the interface point 14 of the photoconductive layer 12. Such an interference of laser beam will occur over the entire surface of the photosensitive member 1 of the photosensitive drum to form a speckled pattern as the result of the interference of laser beam as described above, thus giving rise to density irregularity in the images as the final toner images. In order to overcome such a drawback of the prior art, a proposal has been made to roughen the surface of the electroconductive substrate of the photosensitive member, thereby causing scattered reflection of the light incident on the surface and preventing interference with the light entering the photosensitive member and reflecting from the substrate. However, in a photosensitive member with such a constitution, namely a constitution having an electroconductive substrate with a roughened surface and a photoconductive layer on this substrate, the photoconductive layer may become lower in resistance, depending on the kind of the photoconductive layer employed. As the result, charges are injected from the surface of the photosensitive member into the inner portion thereof, whereby density irregularity is disadvantageously created to form no clear image.